The purpose of this research project is to investigate the details of the coupling between sodium transport and cellular respiration in urinary epithelia using the toad bladder as a model. It had been found previously that sodium transport is tightly coupled to oxygen consumption and to CO2 production. We plan to investigate the various metabolic pathways that contribute to the energy supply of the sodium pump. Total CO2 production will be measured by a conductometric method and simultaneously the rate of oxidation of a number of respiratory fuels will be monitored by an ionization chamber technique. Sodium transport will be measured electrically as the short-circuit current. In these experiments we will expect to find what proportion of the total tissue respiration will be coupled to sodium transport. Further we will study the components of the transport-linked pathways. For instance in preliminary studies we found that glucose appears to contribute more energy to the transport-linked pathways than do fatty acids. The situation appears to be reversed for the basal metabolism; i.e., that fraction of cellular metabolism not coupled to transport.